Electron tube



2,944,180 Patented July 5, 1960 ELECTRON TUBE William R. Wheeler, Saratoga, Calif., assignor to Syl- Vania Electric Products Inc., a corporation of Dela= Filed Apr. 22, 1959, Ser. No. 808,061

4 Claims. (Cl. 313-441 This invention relates to electron tubes and particularly to the electrostatic shielding between the input and output circuits of the tubes.

One of the primary requisites in the design of a radio frequency amplifier pentode receiving tube is the provision, for electrostatic shielding between the anode and control grid. The grid to plate interelectrode capacitance mpst bemaintained low and should be of the order below 0.02 pat. Shielding in the active portion of the tube, that is to say in the region of electron current flow, is atforded by the screen grid, but in conventional tube structure the contributions to capacitances between grid and plate across the top and bottom of the electrode mount, around the sides of the electrodes, and between the leads from the header to the electrodes is appreciable. Consequently, top and bottom shields are provided for shielding the mount structure. In addition, a stem or header shield is used to reduce capacitance between the grid and plate leads. These shields are preferably connected to the suppressor grid. This means the provision of a large number of discrete shielding parts in an electron tube. It is desirable to reduce the number of such parts in any tube design.

It is therefore an object of this invention to produce an electron tube with a single, mount carried, shield which will serve to efficiently shield the input from the output sections of the tube including the leads to the two sections.

It has been found that considerable capacitance coupling between input and output circuits exists by reason of stray capacitances around the periphery of an electron tube mount. By providing an outer shell of metal positioned close to the shield forming part of the mount and by electrically interconnecting the same, it is found that such capacitances can practically be eliminated. Accordingly it is another object of the invention to reduce stray capacitances around the mount.

Also it is an object of the invention to further reduce the number of parts in a tube by making the shield serve as a suppressor grid in the tube.

Other objects of the invention will become apparent upon a consideration of the following specification when taken in conjunction with the accompanying drawing in which:

Fig. 1 is a cross section through the header and envelope of a tube with the mount shown in elevation.

Fig. 2 is a section on the line 22 of Fig. 1.

Fig. 3 is a section on the line 3-3 of Fig. l, and

Fig. 4 is a perspective view of a novel form of suppressor plate.

Now referring to the drawings in greater detail, the electron tube of the invention has much in common with the triode illustrated in the patent to Wheeler, 2,872,609, and reference is made thereto for similar parts which have not been described in detail herein.

A pentode has been selected for the purpose of illustrating the invention, though the electrostatic shield of the invention could be used with triodes, tetrodes or other forms of tubes. In general the pentode comprises a header 10 through which leads G K, H H G P and G extend; a mount indicated broadly as 26 and including a cathode 28 with its heat shield 30; a control grid 32; a second grid 34; a suppressor-shield 36 and an anode 38, these parts being maintained between ceramic spacers 40 and rods 42, much as in the Wheeler Patent 2,872,609. For the purpose of maintaining grid 34 close to grid 32 and yet maintain an adequate sized ceramic spacer 40 between control grid 32 and the screen grid 34 in order to reduce leakage between grids and to reduce interelectrode capacitances, the upper and lower ends of the screen grid are offset from the plane of the screen grid laterals and in a direction away from the control grid. The two grids are connected by straps, respectively, to the G and G pins in the header 10.

The cathode is supported in the exemplification from the two rods 42 in the same indirect manner as is disclosed in the Wheeler patent; and the control grid, screen grid and suppressor grid are strung on the rods in much the same fashion as the screen grid is in the Wheeler patent and are strap connected to the appropriate pins in the headers. The face of the control grid is illustrated in Fig. 2 and comprises a frame 43 with grid laterals 44 brazed thereto, the frame having cross bars 46 and 48 and two upstanding arms 50 straddling the upper rod 42. The control grid also has two legs 52 and 54 straddling the lower rod 42, the leg 54 being longer than the leg 52 and connected by a strap 56 to terminal pin G The suppressor grid-shield 36, as seen in Fig. 4, is essentially a rectangular metallic plate with a window 60 cut out therein of a size to allow the electrons to flow therethrough from cathode to anode, the plate besides having a window has a circular aperture 62 at its lower portion of a size to just snugly accommodate the lower rod 42 and a vertically elongated aperture 64 at its upper portion to laterally snugly accommodate the upper rod 42 but yet allow for some play vertically of the grid-shield. The shield is of a length to extend down to the upper face of the header 10 and is there provided with a horizontal flange 66 extending between the input and output lead-in pins to form an electrostatic shield between them. The suppressor grid is connected by a conductive strap 68 to pin G of the header. The upper end of the shield, to help avoid stray capacitances may have a bent over flange 70 spanning the upper ends of the control and screen grids. The anode 38 is mounted as in the Wheeler patent and is strap connected to the P lead in the header. The heater connected to the pins H and H is located within the cathode and is essentially the same as in the Wheeler patent.

The header 10 has a stepped periphery forming a flange 74 for the seating of a metallic envelope 76 of an internal diameter closely fitting the vertical Wall or riser 78 of the step. A strap 80 connects the G pin with the metal envelope 76 by-passing over the upper surface of the header 10 and then being bent down over the riser 78. If desired, the vertical riser may be slotted as at 82 to partially house the vertical bent portion of the strap 80 so that a good frictional fit between the strap and the metal housing or envelope 76 is attained. When the envelope is sealed to the header, as by brazing, the strap 80, will be brazed to the envelope. Thus the envelope and gridshield are at the same electrical potential. The shield is of a size to almost span the space across the envelope at its chordal position, and comes very close to the side walls and top of the envelope. As a result there is exceedingly little stray capacitance circumferentially of the mount with marked reduction in input-output capacitance.

What is claimed is:

1. An electron tube having a header, a metallic envelope sealed to the header and electrode elements within the envelope which comprise at least a cathode, a control grid, a suppressor grid and an anode, input and output pins extending through the header and connected to the electrode elements, said suppressor grid being in the form of a plate interposed between the control grid and the anode and apertured to allow electron flow from cathode to anode, saidplateextending in all directions beyond the lateral and longitudinal dimensionsof the other electrode elements and close to the inner walls of the metallic envelope, an electrical connection between said plate and envelope, said plate extending down to the upper face of the, header and between the input and output pins, said plate also having an end bent at right angles to the plate with the bent end overlapping the ends of the cathode and control grid, all to reduce intercapacitance between the input and output circuits of the tube.

.2. An electron tube having a metallic envelope and electrode elements therein which comprise at least a cathode, a control grid, a suppressor grid and an anode, said suppressor grid being in the form of a plate interposed between the control grid and the anode and apertured to allow electron flow from cathode to anode, said plate extending in all directions beyond the lateral and longitudinal dimensions of the other electrode elements and close to the inner walls of the metallic envelope and A 7 2,94,4,1s0 it cathode, a control grid, a suppressor grid and an anode, and connections for each with respective leads, said suppressor grid being in the form of a plate interposed between the control grid and the anode and apertured to allow electron flow from cathode to anode, said plate extending in all directions beyond the lateral and longitudinal dimensions of the other electrode elements and interposed between the anode lead and the leads to the cathode and control grid as well as the connections thereto. '4. An electron assembly having electrode elements which comprise at least a cathode, a control grid, a 's'uppressor grid and an anode, said suppressor grid being in the form of a plate interposed between the control grid and the anode and apertured to allow electron flow from cathode to anode, said plate extending in all directions beyond the lateral and longitudinal dimensions of the other electrode elements, and having an end bent at right angles to the plate, said end overlapping the ends of the cathode and control grid, all to reduce'intercapacitance 20 between the input and output circuits of the assembly.

References Cited in the file of this patent UNITED STATES PATENTS Gehrke 1 Oct. 11, 1949 2,820,169 Morris Jan. 14, 1958 2,862,134

Miller Nov. 25, 1958 

